Carrier for records and process of making same



c. J. DIFPEL March 31, 1936.

CARRIER FOR RECORDS AND PROCESS OF MAKING SAME Filed Oct. 12, 1934Patented Mar. 31, 1936 I 1 some I UNITED STATES PATENT orr cs CARRIERFOR RECORDS AND PROCESS Cornelis Johannes Dippel, Elndhoven,Netherlands, assignor to N. V. Philips Gioeiiampenfabrleken, Eindhoven,Netherlands Application October 12, 1934, Serial No. 8,1 In GreatBritain October 27, 19%

11 Claims. (Cl. arc-cc) My invention relates to carriers of records andto the manufacture of same, and more particularly'to carriers for themechanical recording of optically reproducible vibration tracks.

By a vibration track is meant a record of any type of vibration,obtained on a carrier by cutting, indenting, or like mechanicaloperation.

My invention will be described in connection with the recordin'g ofsound vibrations and picture impulses, the vibration track on thecarrier being obtained preferably by a cutting operation with a chiseltype of tool, as described on U. S. Patent 1,919,116 to James A. Miller.Such records are usually reproduced optically, for instance by means ofphotocells and/or are photographicaily copied.

However, it should be well understood that my invention is not limitedto the example given for its IIIUStIatiOIL'bUt-BPDHGS broadly 'tomechanically recorded and optically reproducible vibration tracks.

The quality of such mechanically recorded and;

optically reproducible tracks, as will be more fully explainedhereafter, depends largely on the material of the layer in which thetrack is recorded and which is hereinafter referred to as the cuttinglayer. The best results have been obtained so far with cutting layersformed of gelatin. This material has better cutting prop-- erties and istherefore better adapted for such mechanical recording, than celluloidor other similar photographic materials.

However, even when using gelatin as carriers or cutting layers for suchvibration tracks, serious difiicuities exist, and the object of myinvention is to eliminate, or at least greatly reduce, suchdifliculties.

One of the difllculties arises because of the fact that, when generallycutting this material even with a properly sharpened tool, the surfaceof the vibration track is more or less rough, instead of being smooth.This coarse or rough surface, which appears to the eye as if it werefrosted, is not homogeneously transparent, but diffuses the lightpassing through same.

This roughness or frosted surface of the vibration track affects thepassage of light through it, in thesame manner as does a glass platehaving a frosted surface, 1. e. causes a loss in the light transmittedthrough same, as well as a diffusion and deflection of the light rayspassing same. As is known, a glass plate or disc having a frostedsurface is less transparent to light than is a smooth-surfaced disc ofthe same dimensions, as its frosted surface can be regarded as hibitedby the hydrophil colloids in that state being made up of a large numberof small sur= faces forming various angles with each other, whichreflect the light in different directions;

, thus a portion of the light is lost by reflection at the surface, and.the light which is allowed 5 to pass through the disc is deflected anddifiused.

The coarse or rough condition of the track surface, besides decreasingthe translucency oi the track with a resulting loss of light, alsoresults in a non-homogeneous transparency of the track. In reproduction,such reduced translucency of the track decreases the contrast efiect:also the lack of uniformity in translucency of the track causesdisturbing ground noises, which are especially bothersome for vibrationsof small amplitudes. 7

Furthermore the above stated diffusion and deflection caused by a. roughor frosted track surface, deleteriously influences the quality of thecopies obtained from such a track. In order to obtain a good copy of avibration track of the type discussed, a light beam having parallel raysis used in preference to a beam having dif, fused rays, as in the caseof diffused rays the boundary lines of the track do not appear withsumcient sharpness, thus the desired sharp contrast eifect is notobtained. However with a track having a frosted surface, even when usinga light beam having parallel rays, the rays are deflected and difiusedin their passage through the track; thus the above drawbacks of difiusedlight again occur.

This roughness of the cut track-surface seems to be due to theadhesiveness or stickiness exin which they are used for recording. Thisad-' hesiveness prevents a. cutting tool from removing the material ina. continuous smooth cut. In fact the removal of the material takesplace in the form of short individual cuts and with a hopping or jumpingmovement of the cutting tool.

As is well known from regular metal working practice, such anintermittent cutting process, causes a greater cutting resistance andthus requires greater power than does smooth; continuous cutting.

This increased viscosity or stickiness may also cause a completedislodgement and removal, by the cutting tool, of dirt or otherparticles with which the recording material is contaminated. Due to thefact that these articles are carried along by the cutting tool, so thatits cutting edge is deformed during thefurther recording operation, a'considerable distortion of the boundary 55 lines of the track and theoptical reproduction of such a track may occur.

It seems that this hopping or jumping move- .ment of the tool and theresulting irregular cutting of the material are due to the fact that thevery high pressures exerted by the cutting tool upon the, recordingmaterial, during the recording or cutting operation, causes water to bepressed out of the material forming the cutting layer which increasesthe viscosity or stickiness of the layer at the cutting edge. Thisincrease in viscosity at, the cutting edge is also irregular and ingeneral causes the cutting layer to offer a greater resistance to thecutting tool than does a material having a uniform cutting resistancewhich permits a uniform removal ofthe material by the tool.

I have found that the difiiculties referred to above can be considerablyreduced when according to my invention care is taken that the watercontents of the gelatin layer are such that it is in equilibrium with arelative degree of humidity lying between 20 to 50%. The meaning of thiswill be explained hereinafter. In order that the invention may beclearly understood and readily I a film carrying a mechanically-recordedvibration track, which can be reproduced by means of light passingthrough same, and illustrates the advantages obtained with my invention;

Fig. 4 is a sectional view of the film of Fig. 3 taken along the lineIV-IV, also showing the cutting tool while cutting the track.

I have found that the water contents of the gelatin are of greatimportance for its cutting properties. For every kind of gelatin twolimits for the water contents can be given between which the cuttingperformance can be made with good results. Below the under limit thematerial is too brittle and above the upper limit it is-too sticky whichcauses the above-mentioned difliculties.

Furthermore I have found that the water contents of gelatin depend uponthe relative degree of humidity of the surrounding medium and arenearly. independent of temperature. This relation is for different kindsof gelatin not quite the same, but shows a characteristic conformity. InFig. 1 a oocalled swelling isotherm for a predetermined kind of gelatinis shown. The relative degree of humidity of the surrounding medium(9/90) is set out along the abscissa axis and the water contents of thegelatin as ordinates. The relative degree of humidity of the medium isthe ratio between the existing pressure of the water-vapour in themedium (p) and the saturatlon pressure of the water vapour at thistemperature (m). The degree of humidity may be expressed by aproportional number or in percents; both being commonly used. The termswelling isotherm expresses that the curve is determined by constanttemperature and that the increase of the water contents stands in closeconnection to the increase in volume of the gelatin. The curve shows forevery relative degree of humidity of the medium the water contents ofthe gelatin in the state ofequilibrium.

From Fig. 1 it can be concluded that beginning with absolute dryness of.the gelatin the water contents of the material increase rather rapidlyin relation to the increase of the relative humidity. After reaching arelative degree of humidity of about 0.2 the water absorption occursmore slowly, whereas after reaching a relative degree of humidity of 0.7thespecific increase of the water contents is very great.

' To make the matter more clear, it may be remarked that if gelatin withpredetermined water a relatively long time before the state ofequilibrium is obtained. For determining curves as shown in theaccompanying figures, a long time of observation is necessary. Theadjustment of the water contents of the gelatin to the relative degreeof humidity requires less time, when the condition of the gelatin isdetermined by a point of the upper steep part of the curve than if thecondition is determined by a point on a lower part of the curve. Thematerial becomes more sensitive to moisture if the condition of thegelatin is determined by a point on the upper steep part of the curve.One may Say that the water bound up to a state of equilibrium with arelative degree of humidity of about 0.7 is more strongly bound than isthe water bound above this point.

Whereas the curve from Fig. 1 refers to gelatin in powder state, thecurves in Fig. 2 refer to two kinds of gelatin in plate form. For thisspecimen ofgelatin and treated in the state in which it is used forcutting purposes, the specific increase of the water contents increasesalready if the relative degreeof humidity surpasses 0.55.

As can be seen from the different curves the absolute water contentsdepend upon the state (powder or plate) in whichit is treated as well asupon the defilements or additions, which it contains. All curves,however, have a similar form, and have the common property that betweena relative degree of humidity lying between 0.2 to 0.5 the steepness ofthe curve is minimum. It has been shown that in this field the cuttingproperties are best. If the condition of the gelatine is determined by apoint of the From the characteristic shape of the swelling isotherms ofthe different kinds of gelatin and from the corresponding differentcutting properties, it may be supposed that the condition of the gelatinin the three parts of the curve is different. The condition of thegelatin in which it is suitable for cutting purposes is defined by therelative degree of humidity with which the water contents are inequilibrium, whereas the limits of the absolute water contents varyaccording to the state in which it is used and of the additions.Preferably the gelatin used has water contents in equilibrium with arelative degree of humidity of about 0.3 to 0.4 or 30 to 40%. Thesurrounding medium is not essential and may be air or another gas ormixture, provided it does not chemically affect the gelatin. The cuttingconditions of the recording layer may be further improved by combiningthe measures according to the invention and those described in mycopending U. S. patent ap- 1934, now Patent No. 2,019,215, in which Ipro- 10 contents is brought into an atmosphere with an I r arbitraryrelative degree of-humidity it requires pose to add to the gelatin 9.sulphonated castor oil. The effect of this is,'that the sensitivity tomois-' ture is highly decreased, so that it can longer be exposed toatmospheric conditions without losing taking place during thepreparation of the carrier. For instance, thecarrier can be subjected todrying by passing over it a current of gas having a very low watercontent and with the carrier preferably moving in direction opposite tothe flow of the gas; or the carrier can be passed through a space whichis maintained at a definite, low. degree of humidity-the degree ofhumidity and the time of drying depending mainly upon the material ofthe carrier for example of the kind of gelatin used.

Furthermore, water which is not strongly bound can be removed from thecarrier in other ways, for instance, by passing the carrier, in anair-dry state,- through a bath of alcohol whereby a suitable selectionof the concentration of the alcohol removes the less strongly boundwater to the desired extent.

Of course carriers established in the manner set out above, due to thefact that'they are specially prepared, have water contents, which ingeneral are not in equilibrium with the relative degree of humidity ofthe atmosphere or in other words, the water vapour pressure of thegelatin does not correspond to the water vapour pressure prevailing inthe atmosphere. There-. .fore to prevent a change in their waterpressure,

the carriers according to the invention are preferably protected toprevent a change in their water content, for instance by wrapping themin waterproof material up to the time they are used for recording.However, as the rate of absorp tion or liberation of water is quiteslow, as said already before, no diiiiculties arise because of anyabsorption or liberation of water by the carrier, which may take placeduring the relatively short time required for the cutting operation.

In one embodiment of the invention, the drying of the carrier, in whichthe cutting layer may comprise a. gelatin of medium hardness of the typeused in photography, can be carried .out as follows: Atmospheric air isfiltered and sucked into a drying device, where it is cooled below itsdew point, and from the dew point and the temperature of the air itsdegree of humidity is determined. Thereupon the air is heated so as toreduce its humidity to the desired low value. The so dehumidifled air isthen used for drying the recording material. Good results have beenobtained by passing air so treated, at a rate of about 30 cubic metersper hour through a space having a cross sectional area of about 40 cm.by 40 cm., which space contains the material to be dried at such atemperature that the relative degree of humidity of the air is about 30to when it enters the space.

The carrier shown in Figs. 3 and 4 consists of three superimposedlayers. The base or supporting layer 9 is made of a suitable transparentmaterial, for instance ofcelluloid. The second or cutting layer 2 isalso of transparent material. The material of this layer is gelatin,this being the layer into which the track is cut and with which myinvention is primarily concerned. The top layer 3 is the covering layerand is a comparatively. thin opaque layer applied to layer 2. The toolused for the recording is shown as a chisel M, having two cutting edges4-4, which enclose with each other an angle 20:, of about By moving thechisel perpendicular to .the surface of the carrier in accordance withthe amplitudes of the vibrations to be recorded, a vibration track iscut into the carrier, the width of which varies with the amplitudes ofthe vibration to be recorded, said width variations being anamplification of the amplitudes of the chisel.

In the vibration track so obtained, even the high frequency vibrationshave sufficiently large amplitudes and thus can be better recorded, thanby other. known methods.

While cutting, the chisel removes portions of both the layer. 2 and thelayer 3. The covering layer 3 merely serves to provide a diiference intranslucency of the track and of the back-ground so as to permitreproduction by means of passing light. 'I'hecovering layer 3 mayconsist of a very thin opaque layer of paint, or dye, offeringapractically negligible cutting resistance to the chisel. The actualcutting layer is layer 2, and the track can be cut into this layerbefore the covering layer is applied thereto, in which case an opaquecoating is applied either to the surface of the cut track orthe"background around the cording to my invention, as has beenpreviously stated shows a more or less coarse surface of at least partof the vibration track.

If viewed under a microscopethe track surface appears more or lessgranular, as is indicated in the left side of Fig. 3.

Due to the roughness or coarseness of the track surface, as has beenfully explained, the desired sharp contrast effect is not obtained, andalso loss of light and ground noises result.

Furthermore, due to the adhesiveness or stickiness of the materialof thecutting layer, particles of the layer at the edges or boundaries of thetrack for example dirt particles may be dislodged and carried away bythe cutting tool as indicated at 5, which causes an irregular boundaryline, and

consequently distortions in the reproduction or copying of the record.

All the above dimculties are avoided or greatly reduced by processingthe material of the cutting layer, so as to remove all the watertherefrom which is not strongly bound, by one of the above stateddehydrating steps.

While I have described my invention in a specific application, it can beapplied generally in 'the mechanical recording of opticallyreproducichanical recording of an optically reproducible vibrationtrack, the process which comprises, ap-

plying to a carrier a cutting layer formed of gela- I moisture content.

3. In the manufacture of carriers for the mechanical recording of, anoptically reproducible vibration track, the process which comprisesapplying to a carrier-a cutting layerformed of gelatin,-and reducingfrom said gelatin the water contents to such a degree that it becomes inequilibrium with a relative degree of humidity of 20 to 50%.

4, Invthe manufacture of carriers for the mechanical recording of anoptically reproducible vibration track, the process which comprisesapplying to a carrier a cutting layer formed of gelatin, and reducingfrom said gelatin the water contents to such a degree that it becomes inequilibrium with a relative degree of humidity of 30 to 40%.

5. In the manufacture of carriers for the mechanical recording of anoptically reproducible T vibration track, the process, which comprisesapplying to a carrier a cutting layer formed of gelatin, reducing fromsaid gelatin the water contents to such a degree that it becomes inequilibrium with a relative degree of humidity of 20 to 50%, andprotecting prior to using said carrier to prevent a change in its watercontents.

6. In the manufacture of carriers forthe mechanical recording of anoptically reproducible vibration track, the process which comprisesapplying to a carrier 9. cutting layer formed of gelatin, reducing fromsaid gelatin the water contents to such a degree that it becomes inequilibrium with a relative degree of humidity of to 40%, and protectingprior to using said carrier to prevent a change in its water contents'1. In the manufacture of carriers for the mechanical'recording of anoptically reproducible vibration track the process which comprises,apply ng to a carrier a'cutting layer formed of gelatin, and removingthe excess water from the cutting layer by passing said carrier througha current of dry gas, by moving it in a direction opposite to that ofthe flow of said gas current.

8. In the manufacture of carriers for the mechanical recording of anoptically reproducible vibration track, the process comprising thesteps, applying to a carrier a cutting layer formed of gelatin; suckingfiltered air from the atmosphere into a drying device, cooling said airbelow its dew point, heating said air up to such a temperature that itsrelative degree of humidity is about 30 'to and passing said carrierthrough a current of said dried air in a direction opposite to the flowof said air current.

9. In the manufacture of carriers for the mechanical recording of anoptically reproducible vibration track, the process which comprisesapplying to a carrier :3. cutting layer formed of gelatin, and removingthe excess water from the cutting layer by passing said carrier throughan 7 alcohol bath.

10. A carrier for the mechanical recording of an optically reproduciblevibration track, comprising a cutting layer of gelatin with such watercontents that'it is in equilibrium with a relative degree of hunrdity of20 to 50%.

11. A carrier for the mechanical recording of an optically reproduciblevibration track, comprising a cutting layer of a gelatin with suchwater' contents that it is in equilibrium with a relative degree ofhumidity of 30 to 40%.

" a Commms JOHANNES DIPPEL.

